Method of securing an electrical heater to a heat exchanger



Feb.

965 w. A. CHURCHILL 3,168,775

M HOD OF SECURING AN ELECTRICAL HEATER TO A HEAT EXCHANGER Filed June 17, 1964 INVENTOR.

WALTER A. CHURCHILL United States Patent 3,168,775 METHOD OF-SECURING AN ELECTRICAL HEATER TO A HEAT EXCHANGER Walter A. Churchill, 4 Hillcrest Road, Danvers, Mass. Filed June 17, 1964, Ser. No. 375,793 2 Claims. (Cl. 29155.63)

This application is a continuation-in-part of application Serial No. 162,642 filed December 28, 1961 by Walter A. Churchill and now abandoned.

The present invention relates to a heat exchanger and to the method of making it.

Heat exchangers of the prior artcomprise a supporting member and a cylindrical electrical heater, the supporting member being made of metal and being cast about the heater. It has been found that the active life of these prior art exchangers has been considerably shortened due to comparatively early burning-out of portions of the cylindrical heater. Applicant has found that such burningout is caused by lack of contact between portions of the cylindrical heater and such surrounding material, thus causing voids. Since the presence of such voids prevents the adequate transfer of heat from the heater there occurs a build-up of temperature at the portions of the element where these voids occur to such a degree that burn-out ensues. The heat exchanger of the present invention is of a construction in which the foregoing difiiculties are obviated.

The object of the present invention is the provision of a heat exchanger in which heat-exchanging contact is maintained between a heater and its heat-conducting support along the entire length of. the part of the heater received in such support.

A further object is the provision of a heat exchanger comprising a heat-conducting metallic base or supporting member with a groove therein, a cylindrical electrical heater in the groove, the walls of the groove closely embracing the heater throughout the portion thereof received in the groove.

A still further important object is the provision in a heat conducting supporting member of a heater received in a groove having a cross-sectional dimension greater than that of the open side of the groove, the walls of the groove not only embracing the heater to a degree preventing accidental displacement from the groove but also being in uninterrupted intimate contact with the heater throughout the entire length of the groove.

A still further important object is the provision of a heat exchanger comprising a base of supporting member,

giving a groove therein including an arcuate section terminating in two parallel terminal sections, the arcuate section extending throughout most of the circumference of a circle, and being thereby adapted to transfer heat from a heater in the groove in paths of substantially equal length from the groove to the center of the area enclosed thereby, so that the heating effect for this area is equably distributed.

Still another important object achieved by the present invention is the provision of an improved method of making a heat exchanger by establishing a cylindrical electrical heater in a particularly formed groove of a heat-conducting base or support by a hammering action designed to assure uninterrupted intimate contact between the heater and the groove throughout the length of the latter.

A further important object is that of a method of securing a cylindrical electrical heater having a metallic casing in a heat conducting base member having a groove comprising the steps of enlargement of the cross-sectional area of parts of the groove spaced from the groove edges, disposing the cylindrical electrical heater in the groove and applying pressure to the heater to deform it so that its casing is in uninterrupted tight-fitting engagement with the enlarged portion of the groove throughout its length.

. Other important objects of the invention will be apparent from the disclosures in the specification and in the accompanying drawings in which FIGURE 1 is a partial perspective view of the grooved base plate prior to its modification.

FIGURE 2 is a transverse sectional view of the grooved base plate illustrating the operation of undercutting the groove in the plate.

FIGURE 3 is an enlarged fragmentary sectional view showing the insertion of the heater.

FIGURE 4 is a fragmentary sectional view similar to FIG. 3 showing the application of a hammer tool to the electrical heater.

FIGURE 5 is a fragmentary sectional view showing the relationship of the casing of the heater and the walls of the groove upon completion of the hammering operation.

FIGURE 6 is a perspective view of the finished article.

.With reference to the drawings in greater detail, FIG- URE 1 shows a partial perspective view of the supporting member 1 which may be made of a cast malleable metal, for example an aluminum alloy. The member 1 is cast with the groove 2 which comprises arcuate section 7 terminating in spaced parallel portions 8, the groove being processed to accommodate therein an electrical heater as more particularly shown in FIGURE 6.

Applicants method of securing the heater in the supporting member 1, comprises as a first step, the modi-' fication of the groove 2. As shown in FIGURE 2, this modification involves the undercutting of the opposite side walls of the groove by a suitable tool 3, for example, a rotary grinding tool. This is inserted in the groove and is employed to undercut opposite walls thereof throughout their length. Each of these walls is undercut to a height from the bottom of the groove greater than onehalf the height of the uncut groove. Exemplary groove dimensions may be as follows: In the supporting member 1 as cast, the groove may be /2" wide and /2" deep. This width is increased to /2"+.0l5" or .515" by the undercutting process. As shown in FIGURE 2, the undercutting operation forms opposite cut-away portions or cavities 2' having walls merging with the bottom portion of the groove and forming shoulders 6 with the uncut portions 2" of the groove walls. The portions or cavities 2' of the arcuate portion 7 of the groove 2 curve in two mutually transverse directions; i.e., in directions to conform to the are of the arcuate portion and in directions upwardly from the bottom of the groove.

Applicants second step, illustrated by FIGURE 3, comprises the insertion into the open side of groove 2 of an electrical cylindrical heater 4 of a type well known in the art consisting for example of a metallic tubular casing or sheathing 4 enclosing insulation material 4" surrounding a helically wound electrical resistance wire 4" such as shown in Norton 2,875,312, the heater 4 having a diameter of approximately the width of the uncut portions 2" of the groove 2 and a length somewhat greater than the length of the groove. The heater 4 is then passed through the uncut portions 2" of the groove downwardly until it is received in the undercut portions 2' and rests along the bottom of the groove.

The third step in applicants method is shown in FIG- URE 4 and comprises the application of successive reshaping blows administered to the heater 4. These blows are applied to substantially the entire length of the exposed upwardly facing portion of the casing of the heater by a hammer tool 5 inserted through the open side of the groove 2. The effect of these blows is to cause the heater to be deformed so that side portions of the casing 4 intimately and continuously engage the cut-away portions or cavities 2' of the groove wallsthroughout their entire length, the deformation entailing a flattening of the upper portion of the heater 4 sustaining the hammer blows.

The relationship of the heater to the walls of the cutaway groove portions 2 and of the uncut groove portions 2" is shown in FIG. 5.

The finished article produced by applicants method is shown in FIGURE 6, the base or supporting member 1 having a groove therein comprising arcuate and parallel sections 7 and 8 respectively, all of these groove sections having the cross-sectional formshown in FIG. 5. The heater 4 is disposed in the groove sections in the relationship with the walls theerof as shown by the latter figure and according to the method previously described. This manner of disposal as said before, insures such continuous and intimate contact between the cut-away portions 2' of the groove and the heater as to maintain a homogenous heat exchange relationship throughout the contacting lengths of the groove and the heater, there being a complete absence of voids therebetween.

The end portions of the heater as shown, protrude from the ends of the parallel groove sections'and, if desired, may be provided with conventional terminals. i

As will be apparent, not only will the heater 4 be in intimate and continuous contact along the lengths of the cut-away portions 2' after the hammering operation, but the shoulder portions 6, comprising the intersecting walls of the cut-away portions 2 and the uncut portions 2" of groove 2 will efiectively prevent accidental dislodgement of the heater from the groove. As shown in FIGURE 5, the major portion of the heater 4 lies below the lower ends of the parallel walls 2", the upwardly facing flat portions of the casing 4' of the heater being disposed between these walls. r

It is to be understood that modifications and variations of the disclosed method and of the finished article may be resorted to without departure from the spirit and scope of the invention, such modifications and variations being considered to be within the purview andscope of the appended claims. a r

' What I clairn'is: i

1. The method of securing a cylindrical electrical heater to a base plate of aheat exchanger, said electrical heater comprising resistance wire means and insulation means thereforenclosed by atubular metallic casing, said base plate'being made of cast aluminum alloy and having top and bottom parallel faces, a groove in said plate opening into one of said faces, said groove. being of a width substantially equal tothe diameter of said cylindrical electrical heater, the thickness of said plate between said parallel faces being substantially greater than the depth of 4 said groove, said method including the first step of removing surface portions of said groove by undercutting opposite walls of said groove to form oppositely disposed cutaway portions merging with the bottom portion of said groove, the second step of introducing said cylindrical electrical heater into said groove through the open side thereof and disposing said heater along said bottom portion of said groove intermedate said cut-away portions, the third step of applying successive hammer blows to the upwardly facing portion of said casing of said heater for a distance along the length thereof corresponding to the length of said groove to force the side portions and the bottom portions of said casing of said heater into intimate and continuouscontact with said cut-away portions and said bottom portion respectively of said groove.

2. The method of securing a cylindrical electrical heater to a base member of a heat exchanger, said electrical heater comprising resistance wire means and insulation means therefor enclosed by a tubular metalliccasing, said base member being in the form of a plate of cast aluminum alloy, said plate having upper and lower substantially parallel faces, an arcuate groove in said upper face, the

thickness of said plate between said faces being substan-v tially greater than the depth of said arcuate groove, said method comprising the step of cutting an elongated cavity in each of the opposite walls of said groove, each said cavity extending outwardly of said groove and being equal in length to the length of said groove, the wall of each said cavity merging with the bottom of said groove and being spaced from the open side of said groove, the further step of disposing said cylindrical electrical heater along the' bottom of said groove, the additional step of applying successive hammer blows through theopen side of said groove to substantially the entire length of the upwardly facing section of said casing of said heater to force the side portions of said casing of said heater adjacent said upwardly facing section into intimate and continuous contact with said wallof each said cavity.

References Cited by the Examiner UNITED STATES PATENTS 1,971,723 8/34 ODell.- 2,630,964 3/53 Scheldorf 29- 522 X 2,666,981 1/54 Sandberg 29157.3

l2,732,615 1/56 Sandberg 29-1573 2,823,016 2/58 Greer.

2,875,312 2/59 Norton.

2,940,162 6/60 Sandberg 29-l57.3

2,987,300 6/61 Green 29-522 X 3,000,093 9/61 Wrende'nfors 29522 X JOHN F. CAMPBELL, Primary Examiner. 

1. THE METHOD OF SECURING A CYLINDRICAL ELECTRICAL HEATER TO A BASE PLATE OF A HEAT EXCHANGER, SAID ELECTRICAL HEATER COMPRISING RESISTANCE WIRE MEANS AND INSULATION MEANS THEREFOR ENCLOSED BY A TUBULAR METALLIC CASING, SAID BASE PLATE BEING MADE OF CAST ALUMINUM ALLOY AND HAVING TOP AND BOTTOM PARALLEL FACES, A GROOVE IN SAID PLATE OPENING INTO ONE OF SAID FACES, SAID GROOVE BEING OF A WIDTH SUBSTANTIALLY EQUAL TO THE DIAMETER OF SAID CYLINDRICAL ELECTRICAL HEATER, THE THICKNESS OF SAID PLATE BETWEEN SAID PARALLEL FACES BEING SUBSTANTIALLY GREATER THAN THE DEPTH OF SAID GROOVE, SAID METHOD INCLUDING THE FIRST STEP OF REMOVING SURFACE PORTIONS OF SAID GROOVE BY UNDERCUTTING OPPOSITE WALLS OF SAID GROOVE TO FORM OPPOSITELY DISPOSED CUTAWAY PORTIONS MERGING WITH THE BOTTOM PORTION OF SAID GROOVE, THE SECOND STEP OF INTRODUCING SAID CYLINDRICAL ELECTRICAL HEATER INTO SAID GROOVE THROUGH THE OPEN SIDE THEREOF AND DISPOSING SAID HEATER ALONG SAID BOTTOM PORTION OF SAID GROOVE INTERMEDATE SAID CUT-AWAY PORTIONS, THE THIRD STEP OF APPLYING SUCCESSIVE HAMMER BLOWS TO THE UPWARDLY FACING PORTION OF SAID CASING OF SAID HEATER FOR A DISTANCE ALONG THE LENGTH THEREOF CORRESPONDING TO THE LENGTH OF SAID GROOVE TO FORCE THE SIDE PORTIONS AND THE BOTTOM PORTIONS OF SAID CASING OF SAID HEATER INTO INTIMATE AND CONTINUOUS CONTACT WITH SAID CUT-AWAY PORTIONS AND SAID BOTTOM PORTION RESPECTIVELY OF SAID GROOVE. 